Apparatus and methods for positioning vehicles and the like by triangulation are well known in the art, see for example U.S. Pat. Nos. 3,665,464, issued May 23, 1972, entitled "Method and Apparatus For High Speed Vehicle Position Acquisition," 3,766,552, issued Oct. 16, 1973, entitled "Unified Area Surveillance, Communication and Mobile Station Guidance System," 4,031,535, issued June 21, 1977, entitled "Multiple Frequency Navigation Radar System." Also, projectile scoring systems of the type including a transmitter for illuminating the projectile and a plurality of spaced apart sensors receiving reflected energy from the projectile and connected to provide signals indicative of the time of arrival of the reflected energy at each of the sensors to a computer designed to calculate the position of the projectile relative to the sensors are known.
Timing apparatus utilized in prior art projectile scoring system are constructed to time intervals between sensor signals by means of counting pulses having a constant repetition rate. In all of the prior art systems the counters are started simultaneously by the occurrence of some predetermined event and each of the counters associated with each sensor is stopped when a signal is received from the sensor. Thus, any overrun in the counter causes an error in the system. Further, the counting apparatus is relatively complicated and it is difficult to provide an indication when a projectile falls outside of a predetermined target area.